Facsimile transmission and reproduction



Juhe 27, 1939. M. D. MCFARLANE ET AL v 2,164,038

FACSIMILE TRANSMISSION AND REPRODUCTION Filed Sept. 2, 1936 11 Sheets-Sheet 1 1 ENTORS.

June 27, 1939. M D. McFARLANE ET AL FACSIMILE TRANSMISSION AND REPRODUCTION Filed Sept. 2, 1936 ll Sheets-Sheet 2 FIG. 2.

IN VENTORJ.

June 27, 1939.

M. D. McFARLANE ET AL FACSIMILE TRANSMISSION AND REPRODUCTION Filed Sept. 2, 1936 ESP-GEEK;

11 Sheets-Sheet 3 INVENTORS.

WW @M J1me 27, 1939 M. D. MQFARLANE ET AL 2,164,038

FACSIMILE TRANSMISSION AND REPRODUCTION Filed Sept. 2, 1956 ll Sheets-Sheet 4 FIG. /0.

June 27, 1939. M. D. M FARLANE ET AL FAGSIMILE TRANSMISSION AND REPRODUCTION 11 Sheets-Sheet 5 Filed Sept. 2, 1956 .FIGJJ.

FIG/Z INVENTORS.

June 1939- I M. D. McFARLANE ET AL 2,154,038

FAC'SIMILE TRANSMISSION AND REPRODUCTION Filed Sept. 2, 1936 ll Sheets-Sheet 6 J7 7 7225mm:

June 2 7, 1939. M. D. MCFARLANE ET AL 2,164,038

FAGSIMILE TRANSMISSION AND REPRODUCTION 11 Sheet-Sheet '7 F/GIZA FIG. .2 0.

F/QZ.

INVENTORS.

June 27, 1939. M, D. MCF'ARLANE ET AL 2,164,038

FACSIMILE TRANSMISSION AND REPRODUCTION FfG-ZZ F! G 2a.

N8 My 60 Man INVENTORS.

n 27, 1939. M. D. MCFARLANE ET AL 2,164,038

FAGSIMILE TRANSMISSION AND REPRODUCTION Filed Sept. 2, 1936 ll Sheets-Sheet 9 1N VENT ORS.

June 27, 1939. M. D. M FARLANE ET AL 2,164;038

FACSIMILE TRANSMISSION AND REPRODUCTION Filegl Sept. 2, 1936 ll Sheets-Sheet.ll

millllllflllll FZGI37.

IN VENT 0R5.

Patented June 27} 1939 UNITED STATES FACSIMILE TRANSMISSEION AND REPRODUCTION Maynard D. McFarlane and Edmund H. Hansen, Hollywood, Calif.

Application September 2, 1936, Serial No. 99,086

18 Claims.

This invention relates to improvements in the art of facsimile transmission and reproduction; that is the reproduction at one or more receiving stations of a facsimile or facsimiles of an original subject at a transmitting station. The disclosure of our invention comprises a complete facsimile system, together with improvements in details and parts thereof. The use of the novel methods and apparatus is not however limited to combination with this particular facsimile system; the various parts herein disclosed may be combined in other ways and with other systems; in addition, many novel features herein disclosed find application in allied arts, and the 5 invention is not limited to their use solely in a facsimile system as herein disclosed.

One of the objects of our invention is to provide a simple and flexible means of transmitting pictures or the like from point to point; and to 20 provide a high efficiency of reproduction in making the facsimile of the original subject.

Another object of our invention is to provide a method for an improved utilization of the transmitted signal; and to utilize a picture frequency for control of unit area reproduction, in contradistinction to the usual envelope frequency utilized for this purpose.

Another object of our invention is to provide a simple and direct method of synchronization;

and means to provide a simple and direct method of phasing.

Another object of our invention is to provide a system of facsimile reproduction which may utilize any suitable existing communication circult; and which is simplified so as to be operable successfully by comparatively untrained personnel.

A stillfurther object of our invention is to provide means for the operation of a facsimile system under the conditions specified by the Federal Communications Commission; and to provide means for facsimile transmission over a voice frequency circuit in such a manner as to be non-interfering to other circuits associated 5 therewith.

Other objects of our invention will be set forth in the appended specification, in which,

the principles of our invention is in commercial use. The invention will therefore be described 55 with refe en e to this system, which consists of the photographic reproduction of photographs or other similar matter. Our invention resides primarily in the terminal equipment employed, and not in the communication channels involved. Any suitable wire circuit, or any suitable radio circuit may be utilized for the purpose of carrying this invention into effect. In the commercial form referred to above, standard commercial telephone channels are employed for the transmission of photographs. 10

One feature of our invention is directed to the method of coupling utilized between the fac simile apparatus and the telephone circuit; this coupling is of such a nature as to comply with the rulings of the Federal Communications Comi3 mission, and it is to be understood that the use of this coupling is not a limitation on the scope of the invention, as the other parts thereof may readily be utilized with other coupling means than those designated to comply with the regu- 2Q lations aforesaid.

In order to scan the original subject to be transmitted, we may make use of a rotating drum or cylinder; associated with which is a mechanism giving a relative lateral movement 25 between the drum and the scanning apparatus. This relative movement may conveniently be effected by means of a leacl screw suitably operated to give the desired helical travel of a scanning spot over the surface of the subject to be 30 transmitted. While various novel devices are described herein with special reference to the sending and receiving mechanisms, it is to be understood that there is no limitation in the invention implied by the use of the drum method of scansion. The same principles may be employed with flat-bed, spiral, side-to-side or any other method of scansion which it may be desired to employ;

According to the form of our invention herein described, the original subject tobe transmitted is placed in the transmitting machine and wrapped around the drum. Suitable clips hold this original subject firmly on the surface of the drum. Light from a suitable source is focused to a spot on the surface of this original subject, which may be a picture, photograph or other material to betransmitted. The light is reflected therefrom to a photo-electric cell, and by means of this cell the lights and shades of the original subject are translated into electrical electrical impulses.

For transmission over a telephone line or a similar communication channel, a signal is required which is alternating in character. The 5 1e may be used to secure a pulsating signal from a 5 output of an alternating current generator of signal may be of a constant frequency varied with respect to amplitude; or a constant amplitude varied with respect to frequency; or a combination of the two. The signal may also be of the timed impulse type wherein the duration of each impulse or train of impulses is a measure of the tone value of the unit area under scansion at any particular instant.

A number of methods well known in the art photo-electric cell system; these include an alternating or undulating potential on the photo-electric cell; or the control by the photoelectric cell and a modulating system of the suitable frequency. Alternately, the light source may be alternating in character, or the light path may be interrupted by any suitable means at a point between the light source and the photo-electric cell.

interrupter having the requisite number of holes or slots necessary to produce a series of light impulses on the surface of the photo-electric cell of a frequency suitable for use in the system. As the light, after leaving the interrupter strikes the surface of the original subject to be reproduced before reaching the photo-electric cell, the tone value of each unit area of the original subject serves to control the intensity of the unit light impulse striking the photo-electric cell.

The pulsating electric current from the photoelectric cell is translated into alternating current by the action of the first transformer in the circuit, in accordance with well known principles. This alternating current may then be amplified, and the amplification may' be carried out by means of conventional thermionic tube amplifiers, or by any other suitable means of amplification. After amplification, the signal from the photo-electric cell may be mixed with a starting and synchronizing signal; and these signals are applied through a coupling device to the telephone line, after further amplification if desired.

At the receiving station, there is provided a similar drum and lead screw arrangement to that at the sending station. The drum or cylinder may be contained in a light-tight housing, and has mounted thereon a film having a photographically sensitized surface. is arranged so as to fall on this film, and the relative movements of the said beam and the film surface are so arranged as to be identical, complementary, or proportional to the relative movements of the scanning beam and original subject at the transmitting station. In order that the individual unit areas of the original shall be correctly located in spatialrelationship to each other on the received facsimile, it is necessary -with this system for the transmitting and-receivingcylinders to run in synchronism. Also, in order that the junction of the original subject on the transmitting cylinder shall correspond with the junction of the photographic surface on the receiving cylinder, it is necessary that the two cylinders shall be in phase with each other.

Our invention provides a method of transmitting phasing and synchronizing signals from the transmitting station to the receiving station in A beam of light order to achieve the above results. In the form of the invention illustrated, the phasing is accomplished by the first impulse of the synchronizing signal; this impulse being released to the line automatically at a suitable point to insure the correct phase relationship between the transmitting and receiving cylinders. Our invention is not limited to the use of the particular synchronizing system here shown.

For driving the receiving cylinder and the receiving lead screw, small synchronous motors are used. The power to drive these motors is provided from an amplifier operated by signals received from the transmitting station over the communication channel. 4

Due to the transmission limitations of an ordinary telephone line, and of many of the communication channels available for the purpose of facsimile transmission, we do not attempt to secure a flat frequency transmission characteristic for the whole band of .frequencies involved. Our equipment is peaked to secure the maximum response at the particular frequencies which we utilize. Further, due to the low frequency cutoff of the majority of telephone and other communication channels, we prefer to send a composite synchronizing signal from the transmitting station locatedv in a band of frequencies which is efiiciently transmitted by the communication channel to be used, and utilize a component of this composite signal for the driving of the synchronous motors at the receiving end.

For example, where we use 60 cycle synchronous motors, we prefer not to send a 60 cycle signal over the line, as the line characteristics at this frequency are extremely unfavorable. We therefore combine two higher frequencies, both of which will be transmitted satisfactorily over the circuit, in such a manner as to provide a 60 cycle beat at the receiving station. By use of a suitable network, this beat signal is separated from the two component frequencies and used to drive the motors. Inpractice, we have found the frequencies 540 and 600 cycles to be suitable for transmitting the 60 cycle beat note to the receiver.

Therefore, at the transmitter, we may provide two generators driven in conjunction with the sending cylinder, one generating a frequency of 540 cycles and the other generating a frequency of 600 cycles. A special relay circuit described below may be utilized to keep these synchronizing frequencies off the line until a desired phase relationship exists between the revolving transmitting cylinder and the stationary receiving cylinder. When this condition occurs, the first synchronizing impulse is sent to the receiving station and the receiving cylinder comes up to speed in correct phase relationship with the transmitting cylinder.

The signal is applied to the telephone line. at the transmitter by the coupling device. The telephone circuit, being an ordinary commercial circuit and passing through the ordinary repeaters and other apparatus, transmits the said signal to the receiving point or points; here another coupling coil picks up the signal and applies it to the input of a pre-amplifler. After preliminary stages of amplification, networks in the form of electric wave filters sepa-- rate the picture and synchronizing signals into their respective channels; and after further amplification if required, these two signals are applied to the receiving mechanism to perform their respective functions.

The picture signals, consisting of constant frequency varying amplitude signals as originated in the photo-electric cell at the transmitting station, are applied to a galvanometer unit or light valve by means of which they are caused to control the intensity of a beam of light in such a manner as to! regulate the exposure on a photographic surface on the receiving cylinder. In this particular arrangement, shown here by way of example, these picture signals vary the intensity of a beam of light from a source of constant intensity; they may however be utilized to control the intensity of the source, as for example in the case of a gaseous discharge lamp.

The interrupter disc may be driven by a. constant speed motor, which may be a motor whose speed is adjusted to be sufficiently constant for the purposes required, or may be a synchronous motor driven from the same source as the motor rotating the cylinder. A definite relationship may be established between the speed of the interrupter disc and the speed of the cylinder, so that the light pulses passing through the inter rupter disc fall upon the original subject in such a manner as to divide this surface into a series of unit areas; this implies that there is a fixed relationship between the rotational spacing of the spot hit by each succeeding pulse and the lateral spacing between adjacent turns of the scanning helix. In practice we have found that there are certain wide limitations within which this relationship can best be established.

As the interrupter frequency is also the scanning frequency, the changes which occur in the scansion of a single area have a definite value in the reproduction of the facsimile; and according to our invention, a function of these changes is incorporated in the transmitted signal, and is reproduced by the special arrangement which we may employ of the galvanometer unit or light valve. A full wave galvanometer unit is employed in the reproduction of the facsimile, so that each complete cycle of the alternating current transmitted from the sending station is represented by two exposures on the photographic surface in building up the facsimile reproduction at the receiving station.

It can readily be seen that our invention results in a far higher transmission speed for the same photographic efficiency; in the first plate, the conventional relationship between carrier and modulation frequency is eliminated; and in the second place, the full signal wave is recorded on the photographic surface at the receiving station to provide a greater resolution of the received picture.

Apart from the combination of photo-electric cell and high fidelity transformer and filter at the transmitting station, the above result is secured by means of a special mask or aperture in the receiving unit. The preferred form of receiving unit may consist of a galvanometer, responsive to the interrupter frequency. The signal applied to the galvanometer unit is alternating in character, not pulsating as is common practice with other systems; and this alternating signal swings the reflected beam of light to either transparent side of a central opaque portion of a light aperture. The two sides of the aperture may be identical, similar, or of a variant shape.

It is of importance to note that the function performed by the galvanometer unit or light valve when used in accordance with our invention, differs from the function normally performed by such a mechanism in the same way as a Class B plained, this gives a picture signal of a frequency.

of 1800 cycles per second. This frequency is sufficiently separated in the frequency spectrum fro-m the other frequencies employed to allow for adequate filtering to segregate the synchronizing frequencies and the picture signal frequency at the receiving station.

The two synchronizing frequencies, after being segregated by a band pass filter or by other suitable means, are passed through a filter or tuned circuit which may have the form of a low pass filter of the constant-k or m-derived type. This filter is arranged to pass the beat frequency, and to reject either of the two component frequencies. The result is that the envelope of these two frequencies, or in other words the beat frequency only, is passed through the low pass filter; and, after amplification, this beat frequency may be utilized as driving power for the motor or motors on the receiver.

In the modification of the apparatus illustrated and described herein, two separate motors are provided in the receiving mechanism. One of these motors drives the receiving drum; and the other motor is geared to the lead screw mechanism for controlling the lateral relative motion of the drum and galvanometer unit. As .an alter native to this method of driving'both motors under the control of the received signal, we have found that sufficient accuracy of reproduction may be secured by driving the cylinder motor from the received signal, and by driving the lead screw motor from the local power supply.

As an alternative to providing the complete power for driving the receiving motors from the amplified synchronizing signal, this signal may be utilized to control the speed of a motor or motors whose main source of rotational power is provided from some other source of energy; the synchronizing signals then provide only the power necessary to regulate the speed instead of the total power required.

In conjunction with the photo-electric cell and its amplifier in thetransmitter, we employ a network which'acts as an electric wave filter selective to the scanning frequency. We have found that the use of such a wave filter increases the faithfulness of reproduction of a facsimile due to the elimination from the circuit of spurious signals, of frequencies other than the scanning frequency, introduced by the relative travel of the transmitting cylinder while the original subject thereon is exposed to a light impulse. Intensity changes which occur within the duration of one light impulse are handled by means of the electrical system; other changes which represent a derivative of the picture are'suppressed in order to secure faithful reproduction at the receiving station. The effect of this derivative phenomenon is a complex function of the interrupter frequency, the tone difference, the linear speed, and the capacitative effect of the photo-electric cell itself. In order to minimize the effect of spurious frequencies, we have found it advisable to insert a network whose function is that of a low pass filter, cutting ofi slightly above the upper of the two generator frequencies, in the circuit of the generators at the transmitting end. This filter network tends to reduce harmonic distortion in the output of the generators themselves, and therefore to reduce distortion in the whole synchronizing system.

The generators described in this application are of a type particularly suited to this work. It-is however possible to replace these generators with others of several well known types without departing from the spirit of the invention. The type of generators which we have produced comprise a permanent magnet with adjustable pole pieces, around which pole pieces are located pick-up coils of a suitable impedance. Between the pole pieces passes the toothed edge of an iron disc; the shape of the tooth may be of an involute form. In the mechanical construction. of the generators, arrangements are made for the movement of the pole pieces towards and away from the center of the shaft, whereby a suitable spot can be obtained for the-production of approximately a pure sine wave. The pole pieces are provided with a screw mechanism whereby they can be drawn towards each other or separated, therefore changing the gap between pole pieces and the generator disc to allow for adjustment of the apparatus to the required output.

As the receiver motors are driven by the amplified signal from the transmitter, it can be seen that their speed is controlled directly by the speed of the transmitter motor; as this latter drives the generators which produce the synchronizing signal. For example, where the transmitter motor is a synchronous motor running at 1800 R. P. M. and

by mechanical coupling generating frequencies of 540 and 600 cycles, the beat frequency, which drives the receiver motor is 60 cycles giving a normal speed of 1800 R. P. M. should the speed of the transmitter motor drop to 1770 R. P. M., the 540 cycle frequency will drop to 531 cycles, and the 600 cycle frequency will drop to 590 cycles; the beat between these two frequencies is 59 cycles,

which will give a speed of 1770 R. P. M. to the phone instrument, and also of the telephone line to the exchange; so that by inducing a current or currents into the induction coil, a transfer of energy takes place which employs the signals from the telephone circuits. In the case of the transmitter, the coupling coil becomes the primary of a transformer whose secondary is the telephone induction coil; in the case of the receiver, the coupling coil is the secondary of a transformer whose primary is the telephone induction coil.

The coupling transfer coil may comprise an air core coil, or it may comprise a coil having a laminated core and a winding thereon. The location of the coil with reference to the telephone bell box depends upon the type of bell box employed; adjustment for this feature is however very readily made by a process of exploration whereby the optimum coupling is readily determined. As previously mentioned, in a preferred embodiment of our invention the coupling transfer coil is tuned to be responsive to the particular frequencies which we desire to transmit. This tuning is carried out in conjunction with .the telephone induce tion coil which forms the secondary of the trans-- former so as to secure a peaked response in the telephone line from the signals from the transmitter.

In practice a number of different types of bell boxes are encountered; and the optimum position for coupling has been known to vary with diflferent types of hell boxes. One particular type, which is a standard type used by the American Telephone 8; Telegraph Company, is herein shown with the coupling coils arranged in a suitable position for inducing signals into the line and for picking up signals from the line. It is not essential that the coupling be through the induction coil in the telephone bell box: we have achieved suitable results by placing a coupling coil in an electromagnetic relationship with the receiver coils of the telephone receiver; and we have carried out experiments showing that there are other arrangements possible.

In the accompanying drawings, certain modiflcations of the apparatus are illustrated; the particular form or forms of the invention here described do not however form a limitation of the scope of the invention to the particular apparatus herein shown in the drawings. in which:

Fig. 1 shows a diagrammatic layout of a sending station.

Fig. 2 shows a diagrammatic layout of a receiving station.

Fig. 3 shows an arrangement of parts of a sending unit.

Fig. 4 shows a plan view of a lead screw and associated mechanism for lateral travel. Fig. 5 is an elevation of apparatus shown in Fi 4.

Fig. 6 is an end view of apparatus shown in Figs. 4 and 5.

V Fig. 7 shows a skeletonized view of a galvanometer unit,

Fig. 8 shows one of the masks used in a galvanometer unit.

Fig. 9 shows another of the masks used in a galvanometer unit.

Fig. 10 illustrates a wave form of a picture signal,

Fig, 11 illustrates a wave form of one phonic generator.

Fig. 12 illustrates a wave form of another phonic generator.

Fig. 13 illustrates a wave form of the combination synchronizing signal from two phonic generators.

Fig. 14 shows a skeletonized view of a receiving box.

Fig. 15 shows an elevation of an interrupter disc.

Fig. 16 shows an enlarged portion of a received photographic surface,

Fig. 17 shows one arrangement of coupling coils.

Fig. 18 shows a schematic circuit of coupling Y Fig. 22 shows a method by which the cylinder holding mechanism may be operated.

Fig. 23 shows an arrangement for a receiving coupling coil.

Fig. 24 shows an arrangement for transmitter and receiver coupling coils in relation to a telephone bell box.

Fig. 25 shows a plan view of one of the phonic generators.

Fig. 26 shows a side elevation of Fig. 25.

Fig. 27 shows in chart form a suitable arrangement of bands of frequencies which may be employed,

Fig. 28 shows a type of overall transmission characteristic for the system.

Fig. 29 shows certain filter network characteristics.

Fig. 30 shows other filter characteristics.

Fig. 31 shows an arrangement of a receiver starting mechanism.

Fig. 32 shows a circuit and arrangement of a transmitter starting impulse mechanism.

Fig. 33 shows an arrangement of a light-tight cover on a receiving machine.

Fig. 34 shows a portable receiving box and mount.

Fig. 35 shows a schematic circuit of one arrangement of apparatus.

Fig. 36 shows one type of photo-electric cell.

Fig. 3'7 shows an arrangement of transmitting and receiving mechanism at a single station.

Fig. 38 shows a drive for an interrupter.

Fig, 39 shows a hinged block for control of lateral travel,

Fig. 40 shows a side elevation of Fig. -39.

In Figure 1, an original subject to be transmitted I is wrapped around the sending drum 2, and held in position by suitable clamps I34 and I 35. A light source 4 is contained in a lamp housing 5, which may be provided with a spherical mirror 6. An interrupter disc I chops the light beam at a predetermined frequency; this interrupter I may be driven by a motor 8 and mounted on the plate 9, which is adapted to travel in a lateral direction under the influence of the lead screw I0 which is driven by the gear II.

The cylinder 2 rotates on its axis under the control of the gear I2. Both the gears. II and I2 are driven by the transverse shaft I4 through the gear I5 on the shaft I6 of the motor II.

The shaft l6 carries, in addition to the gear I5, the phonic wheels I8 and 20. Associated with the phonic wheel I8 is the generator I9, and associated with the phonic wheel 20 is the generator 2|. By means of a segmented construction of the wheels I0 and 20, alternating currents of desired frequencies are generated in the coils of the magnetic generators I9 and 2|,

As has been previously mentioned, other arrangements than that shown for the gears I5, I2, and II may be employed, Individual synchronous motors may be used to drive each of the units of the transmitter; or the drives may be combined in any suitable mechanical combination to be driven by one or more motors.

One of the leads from the phonic generators is passed to the relay 22, and thence together with the other lead from the generators I9 and 2|, to the electric wave filter 24. This electric wave filter may be provided with a volume control 25, and it performs the function of removing spuriousv harmonics and other undesired characteristics from the output of the phonic wheel generators.

In one form of the apparatus, the motor I! is a synchronous motor revolving at 1800 R. P. M.

The phonic wheel I 0 has eighteen segments, and the phonic wheel 20 has twenty segments. Thus the generator I9 generates a current. at a frequency of 540 cycles per second, and the generator 2| produces a frequency of 600 cycles per second. It is to be noted that the beat frequency between these two generator frequencies is 60 cycles per second. The network in the filter 24 may be in the form of a low pass filter, cutting of! just above 600 cycles per second.

Figures 25 and 26 show a plan and elevation of a generator I9 and segmented wheel I8. The generator I9 may be provided with an outer casing I00 and a permanent magnet IOI, which may be provided with pole pieces I02. These pole pieces carry screws I04, and mounted thereon are coils I06. A wheel I0 revolves so that its teeth pass between the ends of screws I04. Due to the segmented nature of the wheel III, a pulsating -electro-magnetic fiux is-set up by the magnet IOI through pole pieces I02, screws I04, and the teeth of the wheel I8. This pulsating magnetic flux causes the generation of a corresponding current in the coils I05. The wave shape of this current is dependent upon the shape of the teeth of the wheel I8 and the adjustment of screws I04 relative thereto.

Figure 12 shows a wave shape of a signal from the generator I9; Figure 11 a shape of a signal from the generator 2|. It will be noted by com.- parison of Figures 11 and 12 that the former is of a slightly higher frequency. After combination of the outputs of the two generators, a resultant wave shape of the type shown in Figure 13 is produced. This is a beat frequency, which is the envelope frequency of Figure 13, and which is the desired synchronizing signal which is in this manner to be transmitted to a receiving station, and in the example here given is 60 cycles per second.

The relay 22 is operated through a switch 29 by means of a cam 26 and contact 21. An arrangement of the circuit for this is shown in Figure 32; wherein a cam 26 and associated rider 2'! coact to close the contact I06. The relay 22 is provided with a coil H0 and contacts I01 and I09. In conjunction with the battery I08, a switch 29 and contacts I06 and I01 are so arranged that on the closing of the switch 29 the next make of the contact I06 will energize the coil IIO by means of the battery I08. By the consequent movement of the armature of the relay, the contact W1 is closed and short circuits the contact I06; thus the coil H0 is continually energized from the battery I08 until the switch 29 is manually opened. The energizing of the coil IIO also causes the relay armature to close the contacts I09 and thereby completes the circuit from the generators I9 and 2| through the leads 23.

Thus the train of synchronizing impulses is sent out through the amplifier to the line after the closing of the switch 29 under the control of the relay 22, at a predetermined position in the cylinder revolution which may conveniently'be the moment at which the junction of the original subject passes in front of the light beam; and as previously described this first impulse of the synchronizing signal serves to start the receiving cylinder in its rotation in correct phase relationship with the rotation of the transmitting cylinder. The output of the filter network 24 is passed to the transmitter amplifier by means of the leads 28.

The beam of light from the lamp 4 strikes the surface of the original subject i at a point 30. The light is reflected from the surfaceat this point, and intercepted by the photoelectric cell 3!, which may conveniently be in the form of a cell with a hole for the passage of the light beam therethrough. As previously described, the interrupter 1 breaks up the light into impulses, producing a succession of electrical pulses in the circuit of the photo-electric cell 3|, each electrical pulse being proportional to the tone value of a corresponding elemental area of the original subject i under scansion at the point 30. From the photo-electric cell 3| the leads 32 carry these pulses to the amplifier 34, which may be provided with a volume control 35, which may be used to regulate manually the level of the picture signal. The amplifier 34 converts the pulses from the cell 3| into an alternating current signal, as previously described, and amplifies this signal to the desired level. 9

A typical wave form of the picture signal as generated in the photo-electric cell 3i and passed through the amplifiers is illustrated in Figure 10. It will be seen that the wave of Figure 10 consists of a single frequency whose amplitude is varied in accordance with the lights and shades of elemental areas of the picture or subject to be transmitted; the heights of the waves in this figure being proportional to the tone values, and

each wave corresponding to an individual unit area of the subject under scansion.

The interrupter disc i has, in one machine built according to this invention, 60 openings through which the light may pass. The motor 8 may be a synchronous motor I'GVOlVingjrat 1800 R. P. M. thereforethe output of the amplifier 341s a frequency of 1800 cycles per second, varying in amplitude in accordance with the tone values of successive elemental areas of the original subject.

The amplifier 36 is connected by the leads all to the filter 36; this filter whose function has been previously described may comprise a high pass network; the cut ofi point of which may lie below the frequency generated by theinterrupter disc. The purpose of the network is to remove from the output circuit the signal components which represent the rate of change of the output of the photo-electric cell due to the rotational relationship between the light beam and the picture i mounted on the cylinder.

This filter network 36 may be of the same type as a filter network later referred to in the description of the receiving electrical system. In the particular apparatus we use, the network consists of two T sections in series, having three condensers in series in the upper arm and two inductances in multiple across the two arms.

A power amplifier 38,. which may be of any conventional type of power amplifier having the required input and output characteristics, may be provided to further amplify the picture signals and also to amplify the synchronizing signals if desired. This power amplifier 38 is connected to the filter network 36 by the leads 39, and also to the filter network 26 in the synchronizing circuit by the leads 23. A number of methods of mixing these two signals may be employed, but in the practical equipment which we use we have provided a series circuit for the mixing of these two signals.

The power amplifier 38 is, in this illustration, connected to the coil 4i whereby energy is transferred to the induction coil in the telephone box 42, and thence to the line 44. The telephone instrument is indicated at 43; this instrument performs no useful function in connection with the transfer of energy or the transmission of the picture, except that, if no cut-off switch is provided, it is advisable to cover the mouthpiece of the instrument to prevent the pick-up of extraneous noises which might be superimposed on the telephone circuit. strument should be removed from its hook for the purpose of completing the circuit to the exchange. The power amplifier may be provided with a volume indicator whereby the energy applied to the coil 4| may be measured in order to determine that the correct level is being sent out.

In cases in which the regulations requiring that the connection to the telephone line be without physical contact are waived, it is to be understood that the coupling coil 4| may be dispensed with and the output of the amplifier 38 coupled in any other suitable manner to the telephone line 44. For example, should a repeat coil be used for this purpose, the line 44 will be connected to the secondaryof this repeat coil and the amplifier 38 to the primary. In this case, the output of the amplifier may be reduced in proportion to the increased efiiciency of the repeat coil over that of the transfer coil 4| and the induction coil in the box 42;

Thus the signal, consisting of both picture signal and synchronizing signal, is transferred from the sending machine to the telephone circuits indicated as starting with the telephoneline 44. From this point, the signals pass through the regular telephone equipment of exchanges, networks, repeaters, etc., to the receiving station.

A layout of the system, showing both transmitting and receiving stations connected by a line through the telephone exchanges, is illustrated in Figure 19.

Figure 2 illustrates one form of receiving apparatus which may be employed according to our invention. In this figure, the signals are received over the telephone line Ma, associated coil is the primary. Thus the signals from the r line Ma induce a magnetic field around the induction coil, whose lines of force out the pickup coil 45 in such a way as to induce a corresponding current in the coil 46 and the circuits associated therewith.

The coil 46 is connected by the leads 4'! to the amplifier 48, which is conveniently provided with a volume control 69 for the purpose of controlling the system. This control may be employed in view of the difierence encountered in practice in telephone circuits of difierent characteristics.

The amplifier Z8 is connected to the filter networks 50 and 5!. These networks may be provided with volume controls 50a and 51a for the purpose of balancing the level of the two sets of signals. It has been found in practice that diiferent telephone lines sometimes have difierent frequency characteristics; so that difierent degrees of attenuation are experienced in the picture andsynchronizing signals. This difference is compensated for by the balance achieved by the two volume controls 50a and Sla; although in practice one of these controls may be elimi- Also, the telephone inf sign, and serves to pass the band of frequencies occupied by the picture signal. Since only a single frequency is employed for the transmission of the picture signals, this filter may be one having a narrow range. In practice however, due to variations of the interrupter disc motor 8, and due to frequency changes which occur in the transmission of the signal over a standard telephone circuit, and other causes, we find it desirable to have a network which passes a band of frequencies at this point.

In certain installations, we have found it advantageous to'divide up the work performed by this network 50; and under these conditions an additional network 501) is provided in the circuit 4! between the pick-up coil 45 and the amplifier 48. Under these circumstances, the network 50b is arranged as a low pass filter network to cut off signals above the wanted range; and the network 50 is a high pass filter passing signals above the range of the synchronizing signal. This latter arrangement is illustrated in the accompanying drawings.

The network 50?) finds its best application under circumstances where the receiver is installed in a location which is electrically noisy. For example, in a number of locations high frequency transients are picked up by the telephone line 44a from local sources, or are picked up at some intermediate point and relayed to the line 44a; and the filter 50b serves to remove the components of these transients which are deleterious to the picture.

One half of the filter 5| may conveniently consist of a band pass filter which passes the frequencies generated by the phonic genera-tors at the transmitter for the synchronizing signal. The second half of the filter 5| may consist of a filter or tuned circuit to pass only the beat frequency of these two generator frequencies.

In this manner, the first section of the filter 5| removes from the incoming signal all frequencies except the comparatively narrow band utilized by the two synchronizing frequencies; and the second half of the filter 5| removes both of these two synchronizing frequencies and passes out only the resultant beat frequency, which is the frequency, which as previously described, it is desired to pass to the motors of the receiver.

It is to be noted that by this arrangement of the generators and the filter networks 5| a frequency suitable for running the receiving motors is passed from the transmitter to the output of the filter 5| without at any time having existed as an individual frequency prior to reaching the output of the filter 5|. In other words, the electrical arrangement we have described performs a function which would otherwise be carried out by an elaborate system of modulation and demodulation. Our device as is here described may be replaced by a system of modulation and demodulation, and in practice this has been done; the circuit we have described is however a preferred form as we have found that the results achieved are superior to those of modulation and demodulation.

The output of the filter 50 is connected to the amplifier 52, which may be of any convenient form suitable to raise the level of the signal to the desired operating level- In order to check operation, this amplifier 52 may be provided with a volume indicator 54. The output of the ampliparatus which we employ,

. 7 fier s2 is carried by the leads 5': to the galvanometer unit or light valve 59. A more detailed description of one form of this galvanometer unit which we have found suitable for operation in accordance with our invention is illus-- trated in Figure 7 and described below.

The galvanometer unit 59 converts the electrical impulses carried to it from the amplifier 52 through the leads 51 into variations of the intensity of a spot of light. This spot is projected onto the surface of the cylinder |a whichis adapted to receive a light sensitive photographic material. The cylinder la is enclosed in a lighttight box or cover 60, which has an opening to allow the beam of light from the galvanometer unit 59 to strike the surface of the film on the cylinder la. An arrangement for effecting this is shown in Figure 4.

The apparatus may also be provided with a second light-tight cover 6|. Both these covers may be dispensed with if the machine is operated in a dark room, but when daylight operation is desired, as is frequently the case, light-tight covers are provided. In the commercial form of the apthe box consisting of the cylinder la and light-tight cover 60 is removable from the machine; the cover 6| prevents extraneous light from entering through the opening in the cover 60 when this opening is so arranged as to pass the light from the unit 59. Automatic means for controlling the opening of the shutter in the cover 60 are described in connection with Figure 14, and an arrangement of the outer, cover is shown in Figure 33.

The galvanometer unit 58 is mounted on the slide 9a. This slide has a lateral travel similar to that o'fthe slide 9 at the transmitter. Details of the slide mechanism, and the method in which the slide 9a travels under the influence of the lead screw |Oa are given in connection with Figures 4, 5, and 6.

The picture signals, originating in the photo: electric cell at the transmitter, are thus passed through the system and filter networks into the galvanometer unit and there control the exposure of the photographic film. The second half of the requirement for successful facsimile transmission lies in the correct placing of the individual unit areas in spatial relationship on the receiv ing surface. This may be accomplished by means of the synchronizing signals sent out from the transmitter.

These synchronizing signals, as above de scribed, reach the filter 5|; and the output of the filter 5| is a signal whose frequency is a function of the speed of rotation of the transmitter. This signal is fed into the amplifier 55, which may conveniently be supplied with a volume indicator 56 as a means of observing operating conditions. The amplifier 55 may be of any suitable type which will supply the requisite output level for the operation of the synchronizing motors. From the amplifier 55, the leads 58 carry the amplified signal to the motors 64 and 65, and also to the coil 66.

at the frequency of the beat note of the two generators 9 and 2| of the transmitter. Due to their design, the motors 64 and 65'will run at a synchronous speed which is a function of that of the motor I! on the transmitter, and will faithfully follow any variations in speed in the motor The motor 64 is adapted to turn the lead screw Illa, and hence to control the lateral These motors 64 and 65 may con- 1 veniently be synchronous motors adapted to run travel of the slide 9 :carrying thereon the galvanometer unit 59,, The motor 65 is adapted to rotate the cylinder la, and the gearing between the motor 65 and the cylinder la bears the same relationship as that between the motor I1 and the cylinder 2 does to their respective synchronous speeds; that is, if both thefmotors 65 and I! run at the same speed, the gear ratio between the motor 65 and the cylinder/ la will be identical with that between the motor I1 and the cylinder 2. It is thus seen that the two motors 64 and 65, by controlling the rotationof the ,cylinder Ia and the lateral travel of the unit 59 in exact corresponding relationship to the rotation of the cylinder 2 and the lateral travel of the light spot 30, fulfil the second half of the above mentioned requirement, in that they produce corresponding spatial relationship of the unit areas of the facsimile as compared to the original subject to be transmitted.

In connection with Figure 1, the contacts 26 and 21 and the relay 22 have been described as a 'means for sending the'synchronizing signals out to the line in such a way as to insure correct phasing relationship of the transmitting and receiving cylinders. We find it advantageous to have a mechanism on the receiving cylinder to coact with that at the transmitting station in order to compensate for the effect produced by certain line conditions encountered in practice. These line conditions may have a tendency to vary the amplitude of the first pulse received from the synchronizing signals, and hence to vary the pull-in time of the motors 66 and 65.

A variation of the pull-in time of the motor 6d is not of importance. Under certain circumstances we have found it entirely possible to run the motor 64 from a source of local power without introducing objectionable distortion into the received facsimile. The pull-in time of the motor 65 however, without the additional equipment below referred to, has an effect on the phasing of. the two cylinders. To overcome this objection, we have therefore installed the trip device and relay 66.

As above mentioned, the coil of the relay 66 is connected by means of the lead 58 in parallel with the motors 64 and 65 to the output of the amplifier 55. The relay is provided with an armature H, latch 69, and contact 10. The circuit of the coil 66 is so arranged in conjunction with the contact 10 and, armature II that when the relay is energized by the first pulse of the incoming synchronizing signal, the armature H is drawn away from the contact 10 and the circuit of the coil 66 is thereby opened. The latch 69 prevents the armature H from again making contact at 10 until the relay is manually reset. At the same time as the armature H is drawn away from the contact 10, the latch 68 is drawn from contact with'the flywheel 61 .on the shaft of the cylinder la; thus allowing the cylinder la to rotate under the influence of the motor 65. As shown in Figure 31, the latch 68 and the latch 69 may be mechanically combined into one piece of mechanism.

The coil 66 of this relay is so designed as to operate on a given integrated current, and in this manner the mechanism serves to regulate the starting of. the rotation of the cylinder la to a. definite time value in regard to the starting synchronizing impulse. It will be noted that the circuit through the coil 66 is opened at the contact ID as soon as'the rotation of the cylinder la commences; by this arrangement the load of the relay coilis removed from the synchronizin circuit and the full power output of the ampliher 55 is applied to the motors 64 and 65.-

A suitable form of this trip mechanism and relay is shown in Figure 31. In this arrangement, the latch 69 and the latch 68 are arranged at opposite ends of the same movable member III which is pivoted at the point H2; and the contact referred to'in reference to Figure 2 as between the armature l! and contact 10 is in this arrangement made between contact 16 and the contact H6 carried on the arm Ill. The projection 69 on the arm III is arranged to cooperate with the armature H in such a way that the armature H can only be in its left-hand position when the arm Hi is in its clockwise position. The lefthand position of the armature H and clockwise position of the arm iii are shown dotted. With the arm ill in this position, the latch 68 engages a slot H4 in the flywheel 61 of the receiving cylinder and the circuit between the contact i6 and the contact H6 is. closed.

The operation of the mechanism shown in Figure 31 is as follows.v Upon energization of the coil 66, the armature H is drawn from its left-hand position; thus from the dotted position to the full line position. When it completes its, travel, the end of the armature 1! passes to the right of the latch 69, and, under the influence of the spring i H, the arm It i is rotated in a counterclockwise direction around the pin H2 until the arm Iii abuts the end of the armature ll. When this arm Hi reaches the limit of its travel, the contact between H6 and i9 is opened, the latch 68 is disengaged from the slot H4, and the latch 69 abuts the end of the armature ii, so that the mechanism can not return to its preoperated or left-hand position until the arm Iii is manually reset to allow the armature I! to clear the latch 69. It will be seen that this mechanical locking arrangement keeps the latches in their operated position in spite of the breaking of the current through the coil 66 due to the opening of the contacts H6 and T0.

The slot HQ in the flywheel Bl may be located at a definite angular position with respect to the junction of the film on cylinder la, so that when the motor 65 reaches its synchronous speed the said junction on cylinder la, will pass in front of a beam of. light from the galva nometer unit 59 at the same instant as the junction of the original i on the cylinder 2 passes before the scanning spot 30. This angle has been determined empirically to be about degrees of clock-wise rotation, and may be found to vary slightly with each installation as it is a function of individual motor performance.

Figure 19 illustrates elements of the apparatus previously described with reference to Figures 1 and 2. In Figure 19 the amplifiers and filters 34, 36, 24, 38 at. the transmitter are shown diagrammatically mounted in panel form with a power supply unit P on a standard relay rack. Similarly the receiving amplifiers and filters 48, 50, 5|, 52, 55 are shown mounted on a rack with a power supply Pa.

The telephone line 44 is shown connected to the telephone exchange H9, whence the circuits I20 lead tothe receiving telephone exchange The circuit [20' may be of any suitable form, and may comprise repeater stations, carrier and phantom circuits, cable, open wire lines, and radio links, etc. In this circuit may also be includedbalancing networks, equalizers, and such other apparatus as is required for the correct transmission of the signals from exchange II! to exchange II9a. Exchange IISa is connected to the receiving statoin by the circuit at.

Figure 3 illustrates an elevation of the scanning mechanism shown in plan in Figure 1. A light source 4 projects light through the opening of the interrupter disc 1; light is also reflected onto the surface of this disc by the mirror 6. An elevation of one form of the interrupter disc 1 is shown in Figure 15; wherein a plurality of openings III! are shown arranged towards the outer edge of the disc. These openings are illustrated as slots, because it is preferable that a definite relationship be established between the size of an opening I I8 which passes in front of the light beam and the size of the aperture 18. The slotted arrangement of the openings shown in the disc 1 in the Figure 15 allows a control to be exercised of the size of opening passing through the optical beam, by means of a lateral adjustment of the position of the motor 8 on the plate 9 relative to the location of the lamp house 5.

An optical system illustrated diagrammatically by the lenses 15 and 14 focus a spot of light at the point 30 on the surface of the original to be transmitted I on the drum 2. This light is reflected, and the nonspecular reflection is intercepted by the surface of the photo-electric cell 3|. By arranging the photo-electric cell so that is does not pick up specular reflection, glossy as well as mat prints may be used as the original subject matter I, and thus the arrangement makes it possible to use various kinds of subject matter on the cylinder 2.

A suitable type of photo-electric cell which may be used with this equipment is illustrated in Figure 36. This cell is of the type known as a barrier layer cell, and is a self-generating light operated source of electricity. The essential parts of this cell are shown in Figure 36, wherein the light sensitive surface IBI is shown on the plate I69 held in the housing I68 by the spring I62. Leads 32 from the front and back of the cell carry the cell output to the transformer I61 which may be conveniently a part of the amplifier 34, or

which may be a repeat coil located at any con-.

venient position. In order to secure the nonspecular reflection above referred to, the cell is mounted over the end of'the optical system. In Figure 36, a suitable position of the optical system mounting tube is illustrated at I64.

The interrupter disc 1 is driven at any desired speed by the motor 8; the speed of the disc 1 and the number of openings H8 therein controlling the frequency of the picture signal. A friction drive mechanism which may be used for securing any desired speed of rotation of the interrupter disc 1 is shown in Figure 38, wherein the motor 8 is provided with a friction disc I18 which may be provided with a leather facing I13 if desired, and which, engages a member I11 on the shaft I15 mounted in the bearings I16. The interrupter disc 1 is fastened to the shaft I15, and the speed of the disc is controlled by the relative location of the member I11 with respect to the axis in the motor 8 by adjusting the position of the member I11 on the shaft I15. A set screw may be provided for locking the member I11 in its desired location.

Referring again to Figure 3, the motor 8, and the light housing 5, are mounted upon the base "9. This base 9 is similar in construction to the base 9a described in relation to Figures i, 5, and andfi; the base 9 travels in a direction at right angles to the path of the beam of light on steel balls 16 over the fixed plate 11. To insure correct movement of the plate 9 with reference to the base 11, these balls may travel in grooves, preferably V-shaped, which may be cut into both the plate 9 and the base 11 The lateral travel of the plate 9 and scanning mechanism mounted thereon is controlled by means of a lead screw, which is similar to that shown in connection with Figures 4, 5, and 6; except that the lead screw on the transmitter may be driven by gearing II from the motor I1 and not by an individual motor as shown in connection with the receiver.

A diaphragm 18 in the path-of the light beam adjacent to the lens 14 controls the size of the spot of light 30 on the surface I. The optical system shown is of a conventional type for this class of work.

Figures 4, 5, and 6 show three views of the slide mechanism. These views relate specifically to the receiving structure, but these are identical with the mechanism used for the transmitting structure with the exception of the method of driving the lead screw as above described, and for the fact that the direction of rotation of the transmitting and receiving lead screws may be reversed with respect to their respective cylinders.

This change in direction of rotation is utilized when a photographic negative of the original subject is being reproduced at the receiving station. If a photographic positive is to be reproduced then the relative directions of rotation of the lead screws with respect to their individual cylinders may be the same. Due to the optical reversal of image on a photographic negative however, the arrangement above mentioned of reversing the direction of relative travel and consequent hand of the scanning spiral is used to secure this optical reversal; and under these circumstances, if both cylinders are rotated in the same direction, and both lead screws have the same hand of thread, the direction of rotation of one lead screw should be opposite to that of the other lead screw.

In Figures 4, 5, and 6, the plate 90. travels in a lateral direction over the base 11a. The slide 9a is provided with grooves 19, and the base 11a with grooves 80. In these grooves, and coacting with them are the balls 16a; these balls provide a means for sliding the plate So over the base 11a and for causing its travel to be confined to the desired straight line direction.

In order to prevent the plate 90 from overriding the grooves, we may provide an arm 8|, to which is hinged a second arm 82. The two arms are held together by means of a screw 84, and the arm 82 may be provided with a roller 85 which rides on the undersurface of the base 11a. If desired, this roller 85 may be equipped with a rubber bushing to absorb any inequalities in travel; and similarly the screw 84 may be provided with a spring for the same purpose.

The lateral travel of the slide 9a over the base 11a is controlled by means of the lead screw Illa, which is in this illustration driven by the motor 64. The plate 9a may have a hinged block 86 fastened thereto, which bears on its lower surface a knife edge I19 adapted to cooperate with the threads of the lead screw Illa. By means of the knob 81, the block 86 may be raised from contact with the threads of the lead screw Illa to allow the plate 9a to be manually moved into any desired position. By means of this manual movement, the plate 9a may be moved to the correct starting position for the commence- 

